Refrigeration compressors are used to compress refrigerants, such as chlorofluorocarbons ("CFCs"), as part of a standard vapor-compression refrigeration cycle. Typically, the gaseous refrigerant is mixed with a liquid lubricating medium, such as oil, immediately before entering the compressor. The lubricating medium facilitates easy handling of the refrigerant during compression, and further lubricates the compressor components (e.g. bearings, seals, etc.) to reduced component wear. After compression, the lubricating medium and refrigerant are separated.
Refrigeration compressors typically include a compressor shaft positioned within a compressor housing, and a bearing unit for rotatably supporting the compressor shaft within the housing. The lubricating medium and refrigerant enter the compressor through an inlet port on one side of the bearing unit, and pass through the bearing unit to provide lubrication. A compressor shaft seal inhibits leakage of the lubricating medium and/or refrigerant between the compressor housing and the compressor shaft. Compressor shaft seals typically include elastomer members (e.g., a rubber seal formed around a steel spring) for providing a compliant biasing force to maintain other seal components in their proper position. In addition, compressor shaft seals can include a seal nose made from carbon graphite or leaded bearing bronze. The lead in typical bearing bronze is desirable in that it is believed to improve wear resistance of the seal nose.
Elastomer members in shaft seals can degrade due to long term exposure to high temperatures and pressures and/or due to chemical reaction with certain lubricating mediums and refrigerants, such as hydrofluorocarbons ("HFCs"). In addition, carbon graphite and elastomers can include small gaps or voids that provide a place for small gas bubbles to enter. These small bubbles can expand and contract considerably due to the large pressure fluctuations inherent in compressors. Such expansions of gas bubbles can rapidly deteriorate the material. Further, seal noses made from typical seal nose materials can show excessive wear and can fail prematurely, particularly when used in high temperature and high pressure environments, such as in a compressor used to compress HFC refrigerants.